Method of manufacturing an incandescent lamp

ABSTRACT

An incandescent lamp which comprises phosphorus as a getter obtained by decomposition of phosphrus oxynitride (PON) in the lamp.

United States Patent [191 [111 3,784,275 Wiedijk Jan. 8, 1974 METHOD OF MANUFACTURING AN INCANDESCENT LAMP Inventor: Piet Wiedijk, Emmasingel,

Eindhoven, Netherlands Assignee: U.S. Philips Corporation, New

York, NY. Filed: Apr. 18, 1972 Appl. No.: 245,252

Foreign Application Priority Data References Cited UNITED STATES PATENTS 3,475,072 10/1969 Graves 316/3 1,612,661 12/1926 Sproesser.. 316/18 1,644,712 10/1927 Graaffe 252/1812 1,817,333 8/1931 Zons... 316/25 X Primary Examiner-Roy Lake Assistant Examiner-J. W. Davie Attorney-Frank R. Trifari' [57 ABS'fRACT An incandescent lamp which comprises phosphorus as a getter obtained by decomposition of phosphrus oxynitride (PON) in the lamp.

4 Claims, No Drawings 1" METHOD OF MANUFACTURING AN INCANDESCENT LAMP The invention relates to the manufacture of both gasfilled and vacuum incandescent lamps.

In the manufacture of incandescent lamps it is common practice to provide a getter on the filament, generally red phosphorus or a mixture of red phosphorus and cryolite. The stem and the filament provided with a getter is mounted in the envelope. The lamp is evacuated, filled with a gas, if a gas-filled lamp is concerned, and sealed. Subsequently the lamp is operated while the red phosphorus is evaporated and chemically reacts with oxygen residues still present in the lamp.

During mounting of the stem and evacuation the envelope is generally heated to a temperature of between has been proposed to use PgN as a getter. P N

decomposes at temperatures of more than approximately 750 C in phosphorus and nitrogen and at room temperature it is chemically inactive. Its gettering action may be enhanced by mixing it with aslight quantity i of a material which supplies oxygen upon heating. Its purpose is to obtain rapid formation of a slight quantity of P 0 when P N is decomposed in the'lamp. As is known P 0 is a very satisfactory water vapour getter.

According toanother proposal P N is mixed with a finely divided metal for the purpose of enhancing the decomposition of P- N in phosphorus and nitrogen and for reducing the formation of volatile PN.

An object of the invention is to use a phosphoruscontaining material which need not be mixed with other materials so as to enhance the gettering action.

According to the invention the method of manufacturing both gas-filled and vacuum incandescent lamps in which a phosphorus compound provided in the lamp during manufacture is decomposed after the lamp has been sealed is characterized in that phosphorus oxynitride (PON) is decomposed in the lamp.

Phosphorus oxynitride is found to be very suitable for the envisaged object. It decomposes at temperatures of more than approximately l,000C in phosphorous nitrogen and phosphorus pentoxide. It is chemically nonreactive or little reactive at room temperature and it does not react noticeably with water vapour. It is an amorphous white powder which can be easily obtained in a form in which it is suspensible. Various methods of manufacturing phosphorous oxynitride are known from literature. It may be obtained, for example, by heating phosphorous oxytriamide (PO (NH in a vacuum or in the absence of air.

Phosphorous oxynitride is preferably provided on the filament of an incandescent lamp. To this end a suspension is prepared in a volatile organic solvent. This suspension may be obtained, for example, as follows.

A solvent of cellulose nitrate (12 percent by weight of nitrogen) in methylisobutylketone comprising 39 gms of-cellulose nitrate per litre is prepared. A quantity of 8 gms of phosphorous oxynitride is added per litre to this solution and the entire quantity is ground for 24 hours in a ball mill. If desired, a blackening-preventing getter such as cryolite may be added to the suspension.

The suspension may be provided on the filament in the conventional manner, for example, by immersing the filament mounted on the current conductors of the stem into the suspension. The solvent is subsequently evaporated, for example, by placing the filament in a hot air-stream. The stem is subsequently sealed to the envelope. The lamp is then evacuated and, if a gasfilled lamp is concerned, it is filled with an inert gas such as argon, crypton, nitrogen or a mixture of argon and nitrogen. The lamp is then sealed and is provided with a suitable base having end contacts to which the current conductors are secured.

The lamp is operated at avoltage at which the filament reaches at least a temperature at which phosphorous oxynitride decomposes while'forming phosphorus, phosphorous pentoxide and nitrogen. Since phosphorous pentoxide is formed during .this decomposition, water vapour residues in the lamp are rapidly gettered. The phosphorous evolving during decomposition serves to neutralize oxygen residues in the lamp.

During tests measuring the average lifetime of the lamps, the number of lumens per watt and the percentage of lumens per watt after three-fourths of the lifetime it was found that phosphorus oxynitride and phosphorous nitride (P N yield much better results than are achievable with red phosphorus However, as compared with P N the use of phosphprus oxynitride has the following advantages:

During decomposition the formation of phosphorous pentoxide takes place immediately so that water vapour is rapidly gettered. As regards P N this is only possible after part of the evolved phosphorus has reacted with oxygen until a hygroscopic phosphorous oxide is formed. A

What is claimed is:

1. In a method of manufacturing gas-filled and vacuum incandescent lamps in which a phosphorous compound which is provided in the lamp during manufacture is decomposed after the lamp is sealed, the improvement being the steps of introducing phosphorus oxynitride into the ,lamp during manufacture and decomposing said phosphorous oxynitride after the lamp has been sealed.

2. A method of manufacturing gas-filled and vacuum incandescent lamps comprising the steps of:

preparing a solution of cellulose nitrate in methylisobutylketone;

adding to said solution a predetermined quantity of phosphorous oxynitride;

grinding said solution containing phosphorous oxynitride to form a suspension;

providing said suspension on a filament to be used in an incandescent lamp;

evaporating the solvent from the suspension provided on said filament;

sealing a stern carrying said filament to the envelope;

evacuating said lamp; and

sealing said lamp.

3. The method of claim 2 wherein said cellulose nitrate comprises 12 percent by weight of nitrogen, said solvent-of methylisobutylketone comprises 39 grams of cellulose nitrate per liter and a quantity of 8 grams of phosphorous oxynitride is added per liter of solution.

4. The method of claim 2 also including the step of operating the lamp at a voltage at which the filament at least reaches a temperature at which phosphorous Joxynitride decomposes while forming phosphorous,

phosphorous pentoxide and nitrogen. 

2. A method of manufacturing gas-filled and vacuum incandescent lamps comprising the steps of: preparing a solution of cellulose nitrate in methylisobutylketone; adding to said solution a predetermined quantity of phosphorous oxynitride; grinding said solution containing phosphorous oxynitride to form a suspension; providing said suspension on a filament to be used in an incandescent lamp; evaporating the solvent from the suspension provided on said filament; sealing a stem carrying said filament to the envelope; evacuating said lamp; and sealing said lamp.
 3. The method of claim 2 wherein said cellulose nitrate comprises 12 percent by weight of nitrogen, said solvent of methylisobutylketone comprises 39 grams of cellulose nitrate per liter and a quantity of 8 grams of phosphorous oxynitride is added per liter of solution.
 4. The method of claim 2 also including the step of operating the lamp at a voltage at which the filament at least reaches a temperature at which phosphorous oxynitride decomposes while forming phosphorous, phosphorous pentoxide and nitrogen. 